Method and apparatus for inter-frequency measurements in a communication network

ABSTRACT

In one aspect of the teachings herein, a wireless device operating in a wireless communication network determines the measurement rate to use for making inter-frequency measurements on a given frequency layer, based on a performance requirement specified for that layer. For example, the wireless device uses a higher measurement rate for a frequency layer that has a performance requirement that is higher than the performance requirement specified for another one of the layers on which it is to perform inter-frequency measurements. Correspondingly, in an example scenario, a network node sends measurement configuration information to a targeted device, where that information indicates the layers on which the device is to perform inter-frequency measurements and indicates the performance requirements corresponding to respective ones of those layers. By way of example, the network node may be a base station, a clay, or another wireless device.

RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 14/052,021, filed 11 Oct. 2013, which claims priority to andthe benefit of U.S. provisional paten application Ser. No. 61/866,675,filed 16 Aug. 2013. The entire contents of each of the aforementionedapplications is incorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to wireless communicationnetworks and particularly relates to configuring and performinginter-frequency measurements in such networks.

BACKGROUND

A typical operator today may have GSM, WCDMA/HSPA and LTE carriersoperating simultaneously on different carrier frequencies. Thesedifferent Radio Access Technologies, RATs, and corresponding carriersmay however have different geographic coverage. For instance, LTE may bedeployed in only urban areas, whereas GSM and HSPA coverage may bedeployed in both urban and rural regions.

Furthermore, for LTE, more than forty frequency bands are defined in the3GPP standard, and even if most of them are not universally availablefrequency bands, an operator in the near future may deploy LTE onmultiple carrier frequencies. One or two carriers may be used forcoverage and hence deployed in macro cells, while the remaining carriersmay be used for hot spot or pico cell coverage. This deployment scenariois especially applicable in urban areas where several LTE carriers onadditional frequency layers may be deployed, to provide hot spots inorder to cope with high capacity demand.

FIG. 1 illustrates an example in the context of the above scenario. Inthe diagram, a wireless communication network 10 includes a number oflarge macro cells 12 that are deployed on a first carrier f0. By way ofexample, the diagram shows macro cells 12-1 and 12-2, which have atleast partially overlapping macro—large—coverage areas. One further seesa number of hotspots or pico cells 14, which individually use one of thecarrier frequencies f1, f2, f3 and f4. By way of example, one seeshotspots 14-1 through 14-4 on carrier frequency f1, hotspots 14-5through 14-8 on carrier frequency f2, hotspots 14-9 through 14-12 oncarrier frequency f3, and hotspots 14-13 through 14-15 on carrierfrequency f4.

Several of the hotspot carriers may be deployed in the same coveragearea. That is, a given hotspot 14 operating on one of the hotspotcarriers may overlap geographically with another hotspot operating onanother one of the hotspot carriers. For example, there may beoverlapping hotspot coverage via carrier f1 and f2 in a given coveragearea, while carriers f3 and f4 provide the same or overlapping hotspotservice in another coverage area, etc.

For optimal usage of multiple carriers in deployments such as shown inthe example of FIG. 1, a wireless communication device operating in thenetwork 10 needs to monitor the carriers based on making inter-frequencymeasurements. Based on making these inter-frequency measurements, thedevice reports signal strength for detected cells on respectivecarriers, to a network, NW, node, such as a supporting base station inthe network 10. The NW node then initiates handover, HO, of the deviceto the then-best carrier and cell, as the serving carrier and cell.

However, typical low-end devices are only equipped with one receiver andhence cannot receive on different carrier frequencies simultaneously.Consequently, such a device needs to interrupt its data reception on agiven carrier frequency to perform measurements on other carrierfrequencies. Such measurements are performed using configuredmeasurement gaps, which are specified for use in performing measurementson other carrier frequencies. The 3GPP Technical Specification TS 36.300includes example details regarding measurement gaps, which are periodswhere the device switches off its receiver and transmitter from aserving cell, so that it can receive transmissions from another cell.These gaps are synchronized with respect to the serving base station ofthe device, because the serving base station must know when the devicewill be performing inter-frequency measurements. As is known, RadioResource Control, RRC, signaling is used to configure the gap periodused by the device.

FIG. 2 shows the measurement gap principle as implemented in LTE. A 6 msgap is allocated every 40 ms or every 80 ms, once inter-frequencymeasurement gaps are triggered. The 6 ms gap allows time for the deviceto find synchronization signals and Common Reference Signals, CRS, inthe context of inter-frequency LTE measurements, or to find the samekind of signals in the context of inter-RAT measurements, such as wherethe device makes inter-frequency measurements on WCDMA/HSPA carriers,for example. The gap duration takes switching times into account.

In earlier releases of LTE, inter-frequency measurements in the same RATor across different RATs was mainly used to address the problem of adevice going out of coverage, e.g., going out of a relatively limitedLTE coverage area. This problem was more prevalent in the early days ofLTE deployment, when LTE coverage was initially quite limited and thenexpanded over time. For example, an urban area may have LTE coveragealong with coverage from one or more other RATs, with the LTE coverageending at or around the borders of the urban area. In such cases,inter-frequency measurements would be triggered as the device approachedthe limits of LTE coverage, so that the device began doinginter-frequency measurements and ultimately underwent a handover fromLTE to, say GSM or WCDMA, before going out of the LTE coverage. In suchcontexts, the inter-frequency measurements were only triggered whennecessary, and measurement gaps and corresponding inter-frequencymeasurements were used only when really needed, because measurement gapsreduce the maximum available throughput, and make data scheduling morecomplex.

For example, a network node responsible for data scheduling needs totake the Hybrid Automatic Repeat reQuest, HARQ, round trip times intoaccount and therefore, using LTE timing as an example, the practicalscheduling gap to a device using inter-frequency measurement gaps is tenmilliseconds, based on a six millisecond gap time plus a fourmillisecond HARQ round trip time. This timing translates into atwenty-five percent throughput loss/scheduling time loss, for the caseof forty milliseconds between measurement gaps.

In further detail, a device may monitor several frequency carriers,which may be regarded as frequency layers. In Release 11 of the 3GPPspecification, depending on the device capability, it may be possible tomeasure up to seven different frequency layers, including LTE TDD/FDD,WCDMA, GSM, etc. Each frequency layer requires a certain radio time fordetection and verification of cells on that layer, and the current 3GPPspecification is based on a worst-case scenario with respect to Dopplerand delay spread, as well as Signal to Noise Ratio (SNR) requirements oncells on the layer.

Additionally, as discussed above, gap measurement requirements mainlytarget the coverage problem. Thus, the requirements for inter-frequencymeasurements are conventionally based on detecting rather weak cells onanother carrier frequency, to ensure that a reliable HO can be madeprior to going out-of-coverage on the current carrier frequency. Forexample, with reference to Section 8.1.2.1.1.1 of 3GPP TS 36.133, thecurrent measurement requirements to find a cell is in the order of3.84*Nfreq seconds, where Nfreq is the number of layers needed tomeasure on, and where detection is geared towards the detection of aweak signal, e.g., Es/Iot=−4 dB. Consequently, having several layers, asexemplified in FIG. 1, implies that from a specification point of view,the device may need tenths of seconds in gap mode to find a suitablecell for HO. That time is problematic in terms of capacity reduction andother considerations.

In a known mitigation of such problems, a device may be configured tomeasure only on a subset frequency layers, e.g., on only two frequencylayers among a larger number of available frequency layers. However,this mitigation approach is complicated in a number of respects. Forexample, the network generally will not know which subset of thefrequency layers is most suitable or useful for monitoring by thedevice. For example, with carriers operating at 2-3 GHz, a difference ofonly a few meters in device location may change which frequency fromamong f1, f2 and f3 would be better for the device to camp on.

SUMMARY

In one aspect of the teachings herein, a wireless device operating in awireless communication network determines the measurement rate to usefor making inter-frequency measurements on a given frequency layer,based on a performance requirement specified for that layer. Forexample, the wireless device uses a higher measurement rate for afrequency layer that has a performance requirement that is higher thanthe performance requirement specified for another one of the layers onwhich it is to perform inter-frequency measurements. Correspondingly, inan example scenario, a network node sends measurement configurationinformation to a targeted device, where that information indicates thelayers on which the device is to perform inter-frequency measurementsand indicates the performance requirements corresponding to respectiveones of those layers. By way of example, the network node may be a basestation, a relay, or another wireless device.

In an example, embodiment, a wireless device, such as a 3GPP UserEquipment, UE, is configured to perform a method for performinginter-frequency measurements with respect to two or more frequencylayers. The method includes receiving measurement configurationinformation from anode in a wireless communication network, where themeasurement configuration information indicates a first performancerequirement for making inter-frequency measurements on a first frequencylayer and a different, second performance requirement for makinginter-frequency measurements on a second frequency layer. The methodfurther includes determining first and second measurement rates,respectively, based on the first and second performance requirements,allocating measurement gaps for making inter-frequency measurements onthe first and second frequency layers, respectively, in proportion tothe first and second measurement rates, and performing inter-frequencymeasurements on the first and second frequency layers in therespectively allocated measurement gaps.

In a corresponding example embodiment involving network-side processing,a network node is configured for operation in a wireless communicationnetwork and performs a method that includes determining a firstperformance requirement for making inter-frequency measurements a firstfrequency layer and a second performance requirement for makinginter-frequency measurement on a second frequency layer. The methodfurther includes generating measurement configuration informationindicating the first and second performance requirements for the firstand second frequency layers, respectively. Processing according to themethod additionally includes sending the measurement configurationinformation to a targeted wireless device operating in the wirelesscommunication network, to thereby configure the wireless device to usethe first performance requirement for making inter-frequencymeasurements on the first frequency layer and to use the secondperformance requirement for making inter-frequency measurements on thesecond frequency layer.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled the art will recognize additionalfeatures and advantages upon reading the following detailed description,and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a known arrangement for a heterogeneouswireless communication network.

FIG. 2 is a diagram of a known configuration for performinginter-frequency measurements using configured measurement gaps.

FIG. 3 is a block diagram of an example embodiment of a wirelesscommunication network, including network nodes configured according tothe teachings herein.

FIG. 4 is a block diagram of an example embodiment of a wireless device,such as the one introduced in FIG. 3.

FIG. 5 is a logic flow diagram of an example embodiment of a method ofperforming inter-frequency measurements at a wireless device.

FIG. 6 is a block diagram of an example embodiment of a network node,such as base station, relay node, or other wireless device in theexample network of FIG. 3.

FIG. 7 is a logic flow diagram of an example embodiment of a method at anetwork node of configuring inter-frequency measurements for a targetedwireless device.

FIG. 8 is a plot of example cell detection times in dependence on signalstrength.

FIG. 9 is a diagram illustrating the allocation of measurement gaps forinter-frequency measurements on different frequency layers in proportionto corresponding performance requirements.

FIG. 10 is a logic flow diagram of another example embodiment ofperforming inter-frequency measurements at a wireless device.

DETAILED DESCRIPTION

FIG. 3 illustrates one embodiment of a wireless communication network20, depicted by way of example using nomenclature and arrangementstypical of LTE networks. The network 20 communicatively couples wirelessdevices 22 with one or more external networks 24, such as the Internetor another packet data network, PDN.

The network 20 includes a Radio Access Network, RAN, 26 and a CoreNetwork, CN, 28. For the depicted LTE embodiment, the RAN 26 comprisesan Evolved Universal Terrestrial Radio Access Network or E-UTRAN, andthe CN 28 comprises an Evolved Packet Core or EPC. In this example, theRAN 26 provides service in a number of cells 30 controlled bycorresponding base stations, shown here as “eNBs” or “eNodeBs” 32, inkeeping with the LTE context. Further in keeping with the example LTEcontext, the CN 28 includes a Mobility Management Entity, MME, 34, aHome Subscriber Server, HSS, 36, one or more Serving Gateways, SGWs,38-1, 38-2, and a Packet Gateway, PGW, 40, at the packet interface, SGi,between the CN 28 and the external network(s) 24.

Certain aspects of the network 20 are simplified for purposes ofdiscussion and there may be multiple other entities present in an actualimplementation and/or certain entities or the connections between themmay vary in an actual implementation. Further, given networkimplementations may use other nomenclature or entity arrangements toprovide similar functionality and the teachings herein are not limitedto the example network arrangement depicted in FIG. 3.

In general, each eNodeB 32 provides service in one or more cells 30,which are shown as cells 30-1 through 30-3 for example purposes. Moreparticularly, the diagram illustrates that one or more of the eNodeBs 32may provide multiple cells using different carrier frequencies orfrequency bands/sub-bands. By way of example, one or more of thedepicted eNodeBs 32 use carriers on frequencies f1, f2, f3, meaning thatthere are one or more corresponding cells 30 on each such frequency. Forexample, a given eNodeB 32 may provide three cells 30, with each suchcell 30 operating on a respective one of carrier frequencies f1, f2, andf3. More generally, a given eNodeB 32 may provide any number of cells30, with each such cell 30 operating on a different carrier frequencyand therefore belonging to a different frequency layer.

Of course, other configurations are possible and there may be a mix ofmacro and micro base stations in the RAN 26, e.g., in a heterogeneousnetwork arrangement, such as that shown in FIG. 1. There also may beoverlaid RANs, i.e., different RATs, with each RAT providing cellsoperating according to the particulars of the RAT. In broad terms, then,it will be understood that at one or more given locations within thegeographic coverage area of the network 20, a given wireless device 20may be able to “see” one or more cells on respective ones of multiplefrequency layers, where a “frequency layer” denotes a particular carrierfrequency or frequency band, and where different frequency layers maybelong to the same RAT or to different RATs.

FIG. 4 illustrates an example configuration for the wireless device 22introduced in FIG. 3, where the wireless device 22 includes one or moreantennas 50 and a corresponding communication transceiver 52, whichincludes antenna interface circuitry 54, transmitter circuitry 56 andreceiver circuitry 58. It will be appreciated that the depictedtransmitter circuitry 56 may be realized as a complete transmitterconfigured for operation within one or more supported types of wirelesscommunication networks and, likewise, the depicted receiver circuitry 58may be realized as a complete receiver configured for operation in thesame such network(s). However, certain aspects of transmit and receiveprocessing also may be performed in the depicted control and processingcircuits 60, which are simply referred to as “one or more processingcircuits 60” or “processing circuit(s) 60”.

Indeed, in one embodiment, certain analog and other transmit/receive,TX/RX, circuitry is implemented by way of the depicted transmitter andreceiver circuitry 56 and 58, while baseband digital TX/RX processing isimplemented within the processing circuit(s) 60. It will thus beappreciated that the processing circuit(s) 60 may comprise one or moremicroprocessors, microcontrollers, DSPs, FPGAs, ASICs, or other digitalprocessing circuitry that is configured to carry out inter-frequencymeasurements, including inter-RAT measurements, according to theteachings herein.

In one example, the processing circuit(s) 60 at least functionallyinclude a measurement control circuit 62, which controls inter-frequencymeasurements, e.g., according to a measurement gap configuration. Theprocessing circuit(s) 60 also may include a measurement circuit 64 formaking inter-frequency measurements, e.g., for making signal quality orstrength measurements on different frequency layers. The measurementcircuit 64 also may be at least partly implemented in the communicationtransceiver 52, e.g., to the extent that analog signal measurements aremade.

The wireless device 22 in the illustrated example further includesmemory/storage 66, which comprises one or more types ofcomputer-readable media, and in one or more embodiments includesnon-volatile memory, such as FLASH, EEPROM, etc. The memory/storage 66in at least one embodiment stores a computer program 68. In at least oneembodiment, the processing circuit(s) 60 are configured to carry out theinter-frequency measurement control and processing taught herein, atleast partly based on its execution of the computer program instructionscomprising the computer program 68.

The memory/storage 66 in some embodiments further stores configurationinformation 70, and the wireless device 22 in at least some embodimentsincludes additional processing circuitry and/or interface circuitry 72.Such circuitry includes, for example, application processors, userinterface circuitry, etc. The configuration information 70 comprises,for example, a mapping between indicator values and correspondingperformance requirements, so that the performance requirement for agiven frequency layer may be identified to the wireless device 22 byassociating the corresponding indicator with that frequency layer, e.g.,in a configuration message sent to the wireless device 22.

Regardless of these implementation details, the wireless device 20 isconfigured to perform inter-frequency measurements with respect to twoor more frequency layers, during operation in a wireless communicationnetwork, e.g., while operating in the network 20. The wireless device 22includes the aforementioned communication transceiver 52 and one or moreprocessing circuits 60, where the communication transceiver 52 isconfigured for transmitting signals to the network 20 and receivingsignals from the network 20.

Further, the one or more processing circuits 60 are configured toreceive measurement configuration information from anode in the network20. For example, the node may be a serving base station, a relay, oranother device 22. The measurement configuration information indicates afirst performance requirement for making inter-frequency measurements ona first frequency layer and a different, second performance requirementfor making inter-frequency measurements on a second frequency layer, andthe one or more processing circuits 60 are correspondingly configured todetermine first and second measurement rates, respectively, based on thefirst and second performance requirements, and to allocate measurementgaps for making inter-frequency measurements on the first and secondfrequency layers, respectively, in proportion to the first and secondmeasurement rates. Based on these allocations, the one or moreprocessing circuits 60 are configured to perform inter-frequencymeasurements on the first and second frequency layers in therespectively allocated measurement gaps. Here, it will be understoodthat “performing” the measurements may comprise controlling the receivercircuitry 58 and the measurement circuit 64 according to the gapallocations.

As a working example, the first performance requirement is morestringent than the second performance requirement. Here, the one or moreprocessing circuits 60 are configured to set the first measurement ratehigher than the second measurement rate, so that relatively moreinter-frequency measurements are made with respect to the firstfrequency layer, as compared to the second frequency layer. Inunderstanding this example, consider that in some embodiments the firstand second performance requirements define first and second celldetection times, respectively, or define first and second cell detectionstrengths, respectively, from which the first and second cell detectiontimes are derived.

In some embodiments, a number of predefined performance requirements areknown to the wireless device 22 and the processing circuit(s) 60 areconfigured to determine which predefined performance requirements to useas said first and second performance requirements based on one or moreindicators conveyed in the measurement configuration information. Forexample, the configuration information 70 includes mapping informationthat maps a given indicator value to a respective one of the predefinedperformance requirements. Thus, the measurement configurationinformation may more efficiently convey performance requirements basedon conveying indicators that map to predefined performance requirements.Further, an indication may be implicit—for example, the wireless device22 may assume that a default or nominal performance requirement appliesto inter-frequency measurements on a given frequency layer unless themeasurement configuration information indicates otherwise.

In any case, the processing circuit(s) 60 are configured to allocatemeasurement gaps to respective frequency layers in proportion tocorresponding performance requirements. For example, with respect to twogiven frequency layers referred to for convenience as “first” and“second” frequency layers, the processing circuit(s) 60 are configuredto allocate a first percentage of measurement gaps from among aconfigured plurality of measurement gaps for making inter-frequencymeasurements on the first frequency layer, and to allocate a secondpercentage of measurement gaps from among the configured plurality ofmeasurement gaps for making inter-frequency measurements on the secondfrequency layer. In particular, the first and second percentages areproportional to the first and second measurement rates. As noted, thefirst measurement rate is determined according to a first performancerequirement applicable to inter-frequency measurements on the firstfrequency layer, and the second measurement rate is determined accordingto a second performance requirement applicable to inter-frequencymeasurements on the second frequency layer.

The “configured plurality” of measurement gaps in the above descriptionmay be defined or otherwise known from inter-frequency measurementconfiguration determined by the network 20 and signaled to the wirelessdevice 22. For example, the network 20 may configure the wireless device22 to use make inter-frequency measurements in a 6 ms gap every 40 ms orevery 80 ms, and thus there is a defined number of such gaps over anygiven window of time, and that number of available gaps may be allocatedproportionally, according to the teachings herein.

In a general case, the one or more processing circuits 60 are configuredto make inter-frequency measurements on a number of frequency layers,including first and second frequency layers, according to a number ofdifferent performance requirements, including first and secondperformance requirements that respectively correspond to the first andsecond frequency layers. In this context, the one or more processingcircuits 60 are configured to determine the measurement rate to use foreach frequency layer based on the corresponding performance requirementindicated or otherwise known for the frequency layer.

Of course, the same performance requirement may apply to more than onefrequency layer and in one or more embodiments the one or moreprocessing circuits 60 are configured to use the same measurement ratefor frequency layers having the same performance requirement. Further,in at least one embodiment, the one or more processing circuits 60 areconfigured to group the inter-frequency measurements by at least one offrequency values and radio access technologies (RATs). Using thattechnique, inter-frequency measurements for frequency layers in adjacentor proximate frequency bands are grouped together, and inter-frequencymeasurements for frequency layers on a same RAT are grouped together.

In other words, in one or more configurations of the processingcircuit(s) 60, the wireless device 22 uses adjacent or consecutivemeasurement gaps to make inter-frequency measurements on frequencylayers within the same frequency band or on frequency layers that areordered in terms of increasing or decreasing frequency, which cansimplify or otherwise make receiver frequency adjustments moreefficient. Additionally, or alternatively, the wireless device 22 usesadjacent or consecutive measurement gaps for inter-frequencymeasurements being made on frequency layers within the same RAT, whichminimizes switching back and forth between RATs. In that regard, itshould be understood that the above-mentioned first and second frequencylayers may be on different RATs, or on the same RAT. For a given numberof frequency layers on which the wireless device 22 is to makeinter-frequency measurements, all frequency layers may be on the sameRAT, or they may involve two or more RATS.

FIG. 5 illustrates a method 500 that serves as an example of thecontemplated inter-frequency measurement control and processingcontemplated herein for a wireless device 22. Unless otherwise noted,the illustrated processing steps or operations are not necessarilyperformed in the order illustrated and/or some operations may beperformed in parallel, in the background, or as part of overalloperations at the wireless device 22. Further, the illustrated method500 may be repeated or otherwise performed on an ongoing basis, at leastwhen inter-frequency measurements are activated.

With the above in mind, the method 500 is directed to performinginter-frequency measurements with respect to two or more frequencylayers, and it includes receiving (Block 502) measurement configurationinformation from a node in the wireless communication network 20. Thenode is, for example, a serving base station, such as a serving eNodeB32. The received measurement configuration information indicates a firstperformance requirement for making inter-frequency measurements on afirst frequency layer and a different, second performance requirementfor making inter-frequency measurements on a second frequency layer(Block 502).

Correspondingly, the method 500 further includes determining (Block 504)first and second measurement rates, respectively, based on the first andsecond performance requirements. The measurement rates may be calculatedon the fly, in dependence on the corresponding performance requirements,or the measurement rate to use for a given performance requirement maybe predefined and selected accordingly, e.g., a default measurement ratemay apply to a default performance requirement, with a highermeasurement rate or rate offset defined for a more stringent performancerequirement. In any case, the method 500 includes allocating (block 506)measurement gaps for making inter-frequency measurements on the firstand second frequency layers, respectively, in proportion to the firstand second measurement rates, and performing (Block 508) inter-frequencymeasurements on the first and second frequency layers in therespectively allocated measurement gaps.

FIG. 6 illustrates an example network node 80, e.g., a node that isconfigured for operation in the network 20 and in particular isconfigured to provide the aforementioned measurement configurationinformation to one or more wireless devices 22 operating in the network20. In a non-limiting example, the node 80 can be understood as a givenone of the eNodeBs 32 introduced in FIG. 3. More generally, however, thenode 80 may be any node that is remote with respect to the wirelessdevice 22, such as a base station, a relay node, and even anotherwireless device 22 in device-to-device, D2D, communication.

A communication interface 82 included in the node 80 is configured forsending and receiving signaling, and is operatively associated withprocessing and control circuits 84, which are referred to as “one ormore processing circuits 84” or “processing circuit(s) 84”. In anexample case where the node 80 is a base station or other radio node foruse in a wireless communication network 22, the communication interface82 comprises radiofrequency circuitry, e.g., pools of transmit andreceive circuitry for transmitting broadcast and control signaling, andfor transmitting and receiving user traffic on shared and/or dedicatedchannels. More generally, in such cases, the communication interface 82will be understood as comprising cellular transceiver circuitry forimplementing the uplink/downlink air interface used to connect wirelessdevices 22 to the network 20. The communication interface 82 maycomprise multi-carrier/multi-frequency radio circuits.

Further, in an example configuration, the processing circuit(s) 84include a measurement configuration circuit 86, which is configured toperform the network-side inter-frequency measurement processingconfiguration and control taught herein. The processing circuit(s) 84further include or are associated with memory/storage 88, which maycomprise one or more types of computer-readable media, such asnon-volatile memory, disk storage, etc., and which may also includeworking memory. In some embodiments, the memory/storage 88 stores acomputer program 90 that, when executed by the processing circuit(s) 84configure the node 80 according to the network-side teachings herein. Itwill be appreciated that in an example embodiment, the processingcircuit(s) 84 comprise one or more microprocessors, microcontrollers,DSPs, FPGAs, ASICs, or other digital processing circuitry that isconfigured to carry out network-side processing according to theteachings herein—e.g., to determine the measurement configurations to beused by one or more wireless devices 22 in making inter-frequencymeasurements and to generate and transmit the corresponding measurementconfiguration messages.

Further, in some embodiments, the network node 80 includes additionalcommunication interfaces 92, such as “X2” interface circuitry used toprovide inter-eNodeB communications in an LTE context, and/or one ormore interfaces to other nodes in the CN 28 of the network 20. As notedpreviously, in an example embodiment, the network node 80 is configuredfor operation in the network 20 and the communication interface 82 isconfigured for sending signaling to a targeted wireless device 22. Ofcourse, more than one wireless device 22 can be targeted with respect tothe processing and signaling contemplated herein for configuringinter-frequency measurements at such device.

Continuing with the example, the one or more processing circuits 84 areoperatively associated with the communication interface 82 andconfigured to determine a first performance requirement for makinginter-frequency measurements a first frequency layer and a secondperformance requirement for making inter-frequency measurements on asecond frequency layer. In one example, “determining” a performancerequirement comprises calculating a performance requirement. In anotherexample, “determining” a performance requirement comprises selectingfrom among two or more predefined performance requirements, or otherwiseselecting a performance requirement that is different from a default ornominal performance requirement.

The processing circuit(s) 84 are further configured to generatemeasurement configuration information indicating the first and secondperformance requirements for the first and second frequency layers, andsend the measurement configuration information to a targeted wirelessdevice 22 operating the wireless communication network, to therebyconfigure the wireless device 22 to use the first performancerequirement for making inter-frequency measurements on the firstfrequency layer and to use the second performance requirement for makinginter-frequency measurements on the second frequency layer.

In some embodiments, the one or more processing circuits 84 areconfigured to determine the first and second performance requirementsbased on being configured to set or select a more stringent performancerequirement for the first frequency layer and set or select a lessstringent performance requirement for the second frequency layer, basedon the first frequency layer being associated with a carrier that isdeemed to be coverage related and the second frequency layer beingassociated with a carrier that is deemed to be capacity related. Here, acoverage-related carrier is one that is associated with providingservice in a geographic coverage sense, while a capacity-related carrieris one that is associated with additional service capacity within agiven coverage area and/or a carrier that is intended to providehotspot, overlay, or higher-rate service within a given coverage area.In a non-limiting example, a coverage-related carrier can be aneighbor-cell carrier that is a candidate for handover of the targetwireless device 20.

In at least one embodiment, the one or more processing circuit(s) 84 areconfigured to trigger the targeted wireless device 20 to performinter-frequency measurements, e.g., by sending a configuration messageto the targeted wireless device 20. Further, in at least one embodiment,the processing circuit(s) 84 are configured to send the measurementconfiguration information to the targeted wireless device 22 based onbeing configured to send a measurement configuration message to thetargeted wireless device 22, where that message includes one or moreindicators that indicate first and second performance requirements forfirst and second frequency layers, respectively.

In an example case, the measurement configuration information indicatesthe first and second performance requirements by conveying one or moreindicators having a known mapping to a number of predefined performancerequirements. The measurement configuration information may furtherindicate to the targeted wireless device 22 the frequency layers onwhich the targeted wireless device 22 is to perform inter-frequencymeasurements, including the first and second frequency layers, andindicate the corresponding performance requirement to be used by thetargeted wireless device 22 for making the inter-frequency measurementson each such frequency layer.

FIG. 7 illustrates a method 700, such as may be performed by the networknode 80 introduced in FIG. 6. Unless otherwise noted, the processingsteps or operations may be performed in an order other than thatsuggested by the diagram, and one or more of the operations may beperformed in parallel, for the same or for different targeted wirelessdevices 22, for individual devices or for groups of devices. Further,some or all of the operations may be repeated or performed as needed,and may be performed as part of other processing operations carried outby the node 80.

With the above qualifications in mind, the method 700 includesdetermining (Block 702) a first performance requirement for makinginter-frequency measurements a first frequency layer and a secondperformance requirement for making inter-frequency measurements on asecond frequency layer, and generating (Block 704) measurementconfiguration information indicating the first and second performancerequirements for the first and second frequency layers. The method 700further includes sending (Block 706) the measurement configurationinformation to a targeted wireless device 22 operating in a wirelesscommunication network 20, to thereby configure the wireless device 22 touse the first performance requirement for making inter-frequencymeasurements on the first frequency layer and to use the secondperformance requirement for making inter-frequency measurements on thesecond frequency layer.

In example embodiments in the context of the above discussion andrelated diagrams, a wireless device 22 uses measurement gaps to performmeasurements on different frequency carriers or layers, where thewireless device 22 comprises a communication interface, e.g., atransceiver 52, that is configured to transmit and receive wirelesssignals to and from a wireless communication network 20, and furtherincludes one or more processing circuits 60 that are operably associatedwith the communication interface 52. The processing circuit(s) 60 in anexample embodiment are configured to receive a measurement configurationmessage via the communication interface, where that message definesdifferent performance requirements for the different frequency carriersor layers. Such circuitry is further configured to determine differentmeasurement rates or other measurement configuration parameters for thedifferent carrier frequencies or layers, according to the respectiveperformance requirements indicated by the measurement configurationmessage.

In an example case, the processing circuit(s) 60 determine measurementgap allocations for performing measurements on the different frequencycarriers or layers, in dependence on the different performancerequirements, so that respective ones of the frequency layers havingcomparatively higher performance requirements—more stringentrequirements—have a higher measurement rate than respective ones of thecarriers or layers having comparatively lower performancerequirements—less stringent requirements. For example, the layers havinghigher performance requirements are allocated more measurement gaps thanrespective ones of the layers having relatively lower performancerequirements. The processing circuit(s) 60 are further configured tomeasure—or at least to control measurements on—the different frequencylayers, according to the measurement gap allocations.

In one or more embodiments, the measurement configuration messageindicates carrier types or priorities for respective ones of thedifferent frequency layers, and the one or more processing circuits 60are configured to map the indicated carrier types or priorities topredefined performance requirements and to allocate gaps accordingly. Inat least one embodiment, the measurement configuration message indicatesperformance requirements for respective ones of the different carrierfrequencies or layers in terms of signal detection levels or requireddetection times, and the device generally allocates more measurementgaps to those carrier frequencies or layers having lower signaldetection levels or smaller required detection times.

The indication might also convey type indicators for the frequencylayers. For example, a given frequency layer may be a coverage-typelayer, while another frequency layer may be a capacity-type layer. Thus,the message may indicate the type of a given frequency layer and thedevice may be configured to map the indicated type to a performancerequirement defined for that type. Thus, the measurement configurationmessage may indicate, e.g., “Type 1” for one frequency layer and “Type2” for another frequency layer, and the device may be configured torecognize that the requirement for a Type 1 layer is −4 dB or Tbase=x,whereas the requirement for a Type 2 layer is 0 dB or Tbase=y.

In any case, the example network node 80 is configured for operation ina wireless communication network 20 and includes a communicationinterface 82 configured to transmit and receive wireless signals to andfrom a wireless device 22 operating in the wireless communicationnetwork 20, and one or more processing circuits 84 operably associatedwith the communication interface 82. The processing circuit(s) 84 areconfigured to determine different performance requirements for thewireless device 22, for respective ones among a number of differentcarrier frequencies or layers, to thereby control the measurement ratused by the device 22 for the different frequency layers, such as tocontrol the device's allocations of measurement gaps to the differentfrequency layers. The processing circuit(s) 84 are further configured togenerate a measurement configuration message for the wireless device 22,indicating the different performance requirements, and to transmit themeasurement configuration message to the wireless device 22.

In a more detailed example of the above teachings, consider that Release11 of the 3GPP Technical Specifications define requirements regardingthe time within which a wireless device should detect a newinter-frequency cell, once the signal strength for that cell becomesstronger than a certain level (Es/Iot>b−4 dB). The time is defined as

${T_{{Identify\_ Inte}r} = {{T_{{Basic\_ Identify}{\_ Inter}} \cdot \frac{480}{T_{{Inter}\; 1}} \cdot N_{freq}}\mspace{14mu}{ms}}},$where TBasic_Identify_Inter=480 ms, Tinter1=60 or 30 ms, respectively,depending on whether the 40 or 80 ms inter-frequency gap distanceapplies. Furthermore, Nfreq is the total number of frequency layers thatthe device needs to monitor. Hence, assuming a 40 ms gap period, thedetection time is 3.84*Nfreq seconds and this holds for all cells withEx/Iot>−4 dB, where Es/Iot represents aSignal-to-Interference-plus-Noise Ratio (SINR).

However, cell detection time is heavily dependent on the SINR, as isshown by way of example in FIG. 8, which plots cell detection time as afunction of SINR expressed in dB. In the diagram, T_b and Tb/2 indicatethe time for detection with a certain probability—e.g., a ninety percentprobability—for the different scenarios. Notably, the −4 dB requirementin the current 3GPP specification comes from the assumption thatinter-frequency measurements are only needed for addressing coverageissues. However, in network deployments that use multiple frequencylayers for capacity, a cell detection strength threshold of SINR=0 dB,for example, may be sufficient, and cell detection time might in thatcase be halved, or even further reduced.

Hence, one aspect of the teachings herein involves a new cell detectionrequirement with, for instance, a requirement to detect cells strongerthan, say SINR 0 dB. In that case, T_Basic_identify_Inter may be 240 ms.Of course, that value merely serves as an example, and other oradditional values can be used as performance requirements. The networknode 80 in this sense would configures different frequency layers withdifferent detection requirements. In the example of FIG. 8, it mayconfigured a first frequency layer, f1, with a standard or defaultrequirement of −4 dB, while configuring a second and a third frequencylayer, f2 and f3, with a new 0 dB requirement. Correspondingly, thecontemplated wireless device 22 would, based on these example layers andcorresponding performance requirements, allocate measurement gapsaccording to the layers' respective requirements. For example, thewireless device 22 allocates fifty-percent of the configured measurementgaps to f1, while allocating another twenty-five percent of them to f2and the remaining twenty-five percent to f3. The respective measurementrates, i.e., the number of allocated measurement gaps per time unit,will be different for the various layers. In this example, themeasurement rate of f1 is two times the measurement rate of f2 and f3,reflecting the more stringent detection requirement associated with f1.

This scenario is well illustrated in FIG. 9. Carrier frequency f1 is afirst frequency layer and its performance requirement is based on theRelease 11 cell signal detection strength of −4 dB, which yields a celldetection time requirement of TBasic_Identify_Inter=480 ms. Carrierfrequency f2 is a second frequency layer and its performance requirementis based on a cell signal detection strength of 0 dB, which yields acell detection time requirement of TBasic_Identify_Inter=240 ms. Thesame 0 dB value is used for a third carrier frequency f3, as a thirdfrequency layer on which the wireless device 22 is to performinter-frequency measurements. As such, the cell detection timerequirement for f3 also is 240 ms.

The wireless device 22 thus allocates fifty-percent of the measurementgaps to making measurements on f1, another twenty-five percent of themeasurement gaps to making measurements on f2, and the remainingtwenty-five percent of measurement gaps to making measurements on f3.Advantageously, then, the wireless device 22 monitors three frequencies,f1, f2, f3 in the same time it would take to monitor two frequenciesusing the standard cell detection time for both frequencies. Again, inone or more embodiments, inter-frequency measurements related tocoverage issues will generally receive a greater allocation ofmeasurement gaps than inter-frequency measurements related to capacityissues.

FIG. 10 is a flow chart representing another embodiment of processing atthe wireless device 22. The method 1000 as illustrated in FIG. 10therefore can be understood as an extension or refinement of the method500 introduced in FIG. 5.

According to the method 1000, a wireless device 22 is connected to aserving cell in a wireless communication network 20 and inter-frequencymeasurement has been triggered (Block 1002), either by the wirelessdevice 22—e.g., based on signal strength measurements—or autonomously bythe network 20. The wireless device 22 receives (Block 1004) ameasurement configuration message from the network 20, including, say Nlayers to measure on, together with measurement requirementscorresponding to the respective layers. For instance, the wirelessdevice 22 may receive a matrix of requirements, (f_i, r_i) i=1, . . . N,where f_i corresponds to carrier frequency and r_i corresponds to therequirement. The requirement may be defined as value ofT_Basic_Identify_Inter. In another example, the requirement may be aparameter with two values (1, 2) say, where 1 denotes Release 11requirements, while 2 denotes for a different requirement. Note, too,that the received information may, in addition to indicating therespective frequency layers, indicate the involved RATs.

The wireless device 22 then allocates (Block 1006) measurement gaps torespective ones of the frequency layers according to their correspondingrequirements. For example, for N frequency layers, the number of gapsallocated to layer i should be proportional toAllocated ratio of gaps=r_i/(r_1+r_2+ . . . r_N).

Then the wireless device 22 performs (Block 1008) gap measurements onthe respective layers in the allocated gaps. The allocation may be ofround robin type, but may also use other approaches. The intention isthat over a long time period, the number of gaps is allocated to a givenfrequency layer is in accordance with the corresponding requirement, sothe contemplated method also covers the case where the wireless device22 allocates the first portion of gaps to layer 1, the next portion tolayer 2, etc.

Among the numerous advantages attending the teachings herein,inter-frequency measurements over a given number of frequency layers areperformed faster than would otherwise be possible, to the extent thatone or more of those layers have a performance requirement that iscomparatively less stringent than one or more of the other layers. Fromanother perspective, a wireless device 22 operating according to theteachings herein can make inter-frequency measurements on more layerswithin a given window of time, by making fewer measurements on thoselayers having less stringent performance requirements. These operationsprovide for faster handover and/or allow for less time spent makinginter-frequency measurements.

As such, a wireless device configured according to the teachings hereincan more quickly detect the best carrier from among a number ofcarriers, via inter-frequency measurements, aid at the same timerestrict the number of carriers the device measures on, to therebyreduce the measurement burden imposed on the device. Such techniques mayoffer particular advantages in deployment scenarios where a networkoperator uses several carriers at a certain location, with some of thecarriers allocated to macro cells and others allocated to hot spots,e.g., pico or femto cells.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. A method in a network node configured foroperation in a wireless communication network, said method comprising:determining a first performance requirement for making inter-frequencymeasurements on a first frequency layer and a second performancerequirement for making inter-frequency measurements on a secondfrequency layer; generating measurement configuration informationindicating the first and second performance requirements for the firstand second frequency layers; and sending the measurement configurationinformation to a targeted wireless device operating in the wirelesscommunication network, to thereby configure the wireless device to usethe first performance requirement for making inter-frequencymeasurements on the first frequency layer and to use the secondperformance requirement for making inter-frequency measurements on thesecond frequency layer.
 2. The method of claim 1, wherein determiningthe first and second performance requirements include setting orselecting a more stringent performance requirement for the firstfrequency layer and setting or selecting a less stringent performancerequirement for the second frequency layer, based on the first frequencylayer being associated with a carrier that is deemed to be coveragerelated and the second frequency layer being associated with a carrierthat is deemed to be capacity related.
 3. The method of claim 1, furthercomprising triggering the targeted wireless device to performinter-frequency measurements.
 4. The method of claim 1, wherein sendingthe measurement configuration information to the targeted wirelessdevice comprises sending a measurement configuration message to thetargeted wireless device that includes one or more indicators thatindicate the first and second performance requirements for the first andsecond frequency layers.
 5. The method of claim 1, wherein themeasurement configuration information indicates the first and secondperformance requirements by conveying one or more indicators having aknown mapping to a number of predefined performance requirements.
 6. Themethod of claim 1, wherein the measurement configuration informationindicates to the targeted wireless device a number of frequency layerson which the targeted wireless device is to perform inter-frequencymeasurements, including the first and second frequency layers, andindicates the corresponding performance requirement to be used by thetargeted wireless device for making the inter-frequency measurements oneach such frequency layer.
 7. A network node configured for operation ina wireless communication network, said network node comprising: acommunication interface for sending signaling to a targeted wirelessdevice; and one or more processing circuits operatively associated withthe communication interface and configured to: determine a firstperformance requirement for making inter-frequency measurements on afirst frequency layer and a second performance requirement for makinginter-frequency measurements on a second frequency layer; generatemeasurement configuration information indicating the first and secondperformance requirements for the first and second frequency layers; andsend the measurement configuration information to a targeted wirelessdevice operating in the wireless communication network, to therebyconfigure the wireless device to use the first performance requirementfor making inter-frequency measurements on the first frequency layer andto use the second performance requirement for making inter-frequencymeasurements on the second frequency layer.
 8. The network node of claim7, wherein the one or more processing circuits are configured todetermine the first and second performance requirements based on beingconfigured to set or select a more stringent performance requirement forthe first frequency layer and set or select a less stringent performancerequirement for the second frequency layer, based on the first frequencylayer being associated with a carrier that is deemed to be coveragerelated and the second frequency layer being associated with a carrierthat is deemed to be capacity related.
 9. The network node of claim 7,wherein the one or more processing circuits are configured to triggerthe targeted wireless device to perform inter-frequency measurements.10. The network node of claim 7, wherein the one or more processingcircuits are configured to send the measurement configurationinformation to the targeted wireless device based on being configured tosend a measurement configuration message to the targeted wireless devicethat includes one or more indicators that indicate the first and secondperformance requirements for the first and second frequency layers. 11.The network node of claim 7, wherein the measurement configurationinformation indicates the first and second performance requirements byconveying one or more indicators having a known mapping to a number ofpredefined performance requirements.
 12. The network node of claim 7,wherein the measurement configuration information indicates to thetargeted wireless device a number of frequency layers on which thetargeted wireless device is to perform inter-frequency measurements,including the first and second frequency layers, and indicates thecorresponding performance requirement to be used by the targetedwireless device for making the inter-frequency measurements on each suchfrequency layer.